He said in his bidding: "The Great War was over. Lives, friendships, families, societies, nations had been shattered. Everything had changed.

"On this day two years later and at this hour, an unknown warrior, chosen at random to represent all those of these islands who had fought and died, accorded the highest honour of a state funeral, was buried here.

"His grave was to become the focus of our national remembrance and to have international significance.

"Now that the last of his comrades in arms has gone to his eternal rest, we are here once more to remember.

"We remember, with grief, the gas and the mud, the barbed wire, the bombardment, the terror, the telegram; and, with gratitude, the courage and sacrifice.

"Never again, they said; the war to end all wars. With resolution we remember."

Gordon Brown, the Prime Minister, and the Duchess of Gloucester, patron of the World War One Veterans Association, were among the British and foreign dignitaries at the service.

The head of the armed forces, Air Chief Marshal Sir Jock Stirrup, attended alongside the chiefs of staff of the Royal Navy, Admiral Sir Mark Stanhope, the Army, General Sir David Richards, and the Royal Air Force, Air Chief Marshal Sir Stephen Dalton.

Members of the public from across Britain with links to the conflict were also invited.

The beginning and end of the two-minute silence was marked by gunfire from the King's Troop Royal Horse Artillery, fired from Horse Guards Parade.

Bob Ainsworth, the Defence Secretary, who was among the congregation, paid tribute to those who fought in the First World War.

He said: "The war left an enduring impact on those who survived. They were determined that the sacrifices made by those who lost their lives would never be forgotten.

"Today we join together as a nation to honour that promise, and we will always do so".

Sir Jock added: "During the First World War the British military lost some two-thirds of a million dead – nearly 20,000 of those on just one day at the Battle of the Somme.

"These are numbers that are all but incomprehensible to us today. The total amounted to almost one in every 50 people in the land – hardly a community was untouched.

"Such sacrifice must never be forgotten, and today is an important part of that ongoing remembrance".

Also attending the service were former prime ministers Baroness Thatcher and Sir John Major. Tony Blair was unable to attend because he was visiting the Middle East in his role as Quartet envoy.

Others attending included television presenter Michael Palin, journalist and broadcaster Ian Hislop, and Peter Owen, the nephew of First World War poet Wilfred Owen.

The Archbishop of Canterbury described the First World War as a "huge collective bereavement".

Dr Rowan Williams praised the achievement of the 1914/18 generation in repairing some of the "shattered idealism" that characterised the post-war period.

He said: "Some, at least, of those who tried to make sense of where God had been in all this realised that losing the safe, problem-solving God who protected nations and empires might itself be a gift, a moment of truth that brought the reality of God closer, recognised or not."

The Archbishop used his sermon to warn of the "readiness to forget the hard lessons learned by those who had been on the front line" that was prevalent in the 20th century.

He concluded: "The generation that has passed walked forward with vision and bravery, and held together the bonds of our society, our continent, our Commonwealth, through a terrible century.

"May we learn the lessons they learned, and God save us from learning them in the way they had to."